Assimilation rates of dissolved organic carbon by photomixotrophic estuarine phytoplankton

浮游植物传统上被视为水生食物网基础的初级生产者，为更高的营养水平提供能量来源。 然而，一些浮游植物物种的功能，作为初级生产者和异养次级消费者。 具有光合能力但也吸收和同化有机化合物的浮游植物被归类为兼性混合营养生物，或者更简单地说，光混合营养生物。不幸的是，我们目前很少有浮游植物群落的比例，作为光合混合营养体的功能，其次级生产率，或其丰度的时间变化的估计。 目前关于海洋系统营养动力学的范例没有考虑浮游植物能量流的这一潜在的重要替代途径。 这意味着我们可能错过了一个重要的，基本的过程，影响碳循环和河口系统的营养动力学。 此外，由于人为改变DOC组成的变化可能会导致浮游植物群落结构的变化，并可能促进有害藻华物种的增殖。 在生态系统功能方面，即使是温和的光混合营养率可能会改变我们目前的理解浮游植物生产力，整体C营业额，竞争性的相互作用，在河口环境中的能量转移。该项目将使用一种新的方法来提供定量措施的原位率和幅度的兼性异养在自然，河口浮游植物群落在季节性的时间尺度在一个有代表性的河口生态系统。该项目将利用独特的14 C放射性标记技术来量化DOC的原位同化率河口光合混合营养体和估计的DOC转化为浮游植物生物量的光合混合营养在季节性的时间尺度。 这些信息将提供新的见解，碳动力学在河口，DOC的贡献河口食物网，并在确定河口浮游植物群落的结构和功能特征的重要性的光混合营养。智力优势。 该研究将为C（DOC）的替代来源和浮游植物生产途径的潜在重要性提供新的见解。 成功的示范，河口浮游植物的生产的一个重要组成部分是由photomixotrophy将有重大影响的方式，我们目前认为在这些系统中的C流。 该项目有一个合理的可能性，改变目前的范例河口初级生产力，以及提供新的证据浮游植物物种之间的竞争性相互作用的机制，在混合，自然组合。这项研究还将提供一阶近似的不稳定DOC营业额的浮游植物，将是为数不多的测量河口。 研究结果将有助于提高相关的和潜在的生态生理学，有机体和社区层面的过程，涉及碳循环在河口环境中的知识。 该项目将解决更广泛的影响标准，促进发现和理解，同时促进教学，培训和学习。 该项目将为研究生提供支持，为本科生助理提供暑期支持，并让高水平的本科生作为实验室实习生参与其中。 从南加州大学海洋科学项目招募的本科实习生将参与样本分析并学习操作实验室仪器。此外，现场生物测定将作为一个模块添加到所需的海洋科学本科实地课程，MSCI 460 -现场实验室调查。

Phytoplankton, traditionally viewed as primary producers at the base of aquatic food webs, provide an energy source for higher trophic levels. However, some phytoplankton species function as both primary producers and heterotrophic secondary consumers. Phytoplankton that are photosynthetically competent but also take up and assimilate organic compounds are classified as facultative mixotrophs or, more simply, photomixotrophs. Unfortunately, we currently have few estimates of the proportion of the phytoplankton community that function as photomixotrophs, their rate of secondary production, or their temporal variation in abundance. Current paradigms about trophodynamics in marine systems do not consider this potentially important alternative pathway for energy flow for phytoplankton. The implication is that we may be missing a significant, fundamental process that affects carbon cycling and trophodynamics in estuarine systems. Furthermore, changes in the DOC composition due to anthropogenic alterations may result in changes in phytoplankton community structure and possibly promote the proliferation of harmful algal bloom species. In terms of ecosystem function, even moderate rates of photomixotrophy could potentially alter our current understanding of phytoplankton productivity, overall C turnover, competitive interactions, and energy transfer in estuarine environments. This project will use a novel approach to provide quantitative measures of the in situ rates and magnitudes of facultative heterotrophy in natural, estuarine phytoplankton communities over seasonal time scales in a representative estuarine ecosystem. The project will utilize a unique 14C radiolabeling technique to quantify the in situ assimilation rates of DOC by estuarine photomixotrophs and estimate the amount of DOC converted to phytoplankton biomass by photomixotrophy over seasonal time scales. This information will provide new insights into carbon dynamics in estuaries, the contribution of DOC to estuarine food webs, and the importance of photomixotrophy in determining the structural and functional characteristics of estuarine phytoplankton communities. INTELLECTUAL MERIT. The research will provide new insights into the potential importance of an alternative source of C (DOC) and pathway for phytoplankton production. Successful demonstration that a significant fraction of the production of estuarine phytoplankton is by photomixotrophy would have major implications for the way we currently view C flow in these systems. The project has a reasonable likelihood of altering the current paradigms for estuarine primary productivity as well as providing new evidence for mechanisms of competitive interactions between phytoplankton species in mixed, natural assemblages. The study will also provide first-order approximations of labile DOC turnover by phytoplankton and will be one of the few measurements ever obtained for an estuary. Research results will contribute to an improved knowledge of relevant and underlying ecophysiological, organismal, and community-level processes involving carbon cycling in an estuarine environment.BROADER IMPACTS. This project will address the broader impacts criterion of advancing discovery and understanding while promoting teaching, training, and learning. The project will provide support for a graduate student, summer support for an undergraduate assistant, and involve upper level undergraduates as lab interns. Undergraduate interns, recruited from the Marine Science Program at USC, will participate in sample analyses and learn to operate laboratory instrumentation. Furthermore, the field bioassays will be added as a module in a required Marine Science undergraduate field course, MSCI 460 - Field & Lab Investigations in MSCI.